A portion of the disclosure of this patent document and its figures contain material subject to copyright protection. The copyright owner has no objection to the facsimile reproduction by anyone of the patent document or the patent disclosure, but otherwise reserves all copyrights whatsoever.
1. Field of the Invention
This invention generally relates to measuring and testing electricity and, more particularly, to sensors, to probes, and to arrays of probes and sensors for detecting and for mapping electromagnetic fields.
2. Description of the Related Art
The mapping of electromagnetic field vectors is extremely difficult and complex. xe2x80x9cMappingxe2x80x9d refers to describing the magnitude and direction of electromagnetic field vectors. Once the components of an electromagnetic field vector are known, electromagnetic fields may be expressed at a location and time. Electromagnetic fields, however, are often extremely complex to mathematically describe. Analysis of the electromagnetic field vector may require differentiation, integration, gradient, and divergence operations of vector components over lines, surfaces, and three-dimensional volumes. This analysis is considerably complicated when the line, surface, or volume is complexly shaped and cannot be described using mathematics. Electromagnetic field mapping is also used to detect and diagnose flaws in electrically conductive materials, such as cracks, corrosion, holes, or material inhomogeneities. Therefore, experimental measuring of electromagnetic fields is essential to map those fields produced by sources of complex geometries that are difficult to describe theoretically, or to detect fields that can be produced by unknown sources.
In general, a magnetic sensor is used to experimentally measure electromagnetic fields. The sensor is placed within the electromagnetic field and measurements are taken. There are, however, several problems with existing electromagnetic sensors. Although the prior art sensors may be designed to measure electromagnetic fields in one dimension, the prior art sensors are still sensitive to electromagnetic field vector components in other dimensions. Another problem is frequency dependence of existing inductive sensors. Many existing inductive sensors only have an adequate output over a preferred frequency range. If the frequency of the electromagnetic field lies outside the preferred frequency range, the sensitivity of existing inductive sensors are greatly reduced and measurements are lost or compromised. Thus, although sensors are often used to measure complex electromagnetic fields, these problems with existing sensor designs still present limitations in the measurement of electromagnetic fields.
There is, accordingly, a need in the art for improved electromagnetic sensors which substantially isolate individual components of electromagnetic field vectors, electromagnetic sensors which are sensitive over a wide range of frequencies, electromagnetic sensors with a compact design, electromagnetic sensors which are cost effective to manufacture and to use, and electromagnetic sensors that can be manufactured in two-dimensional and three-dimensional arrays.
The aforementioned problems are reduced by sensors of the present invention. A sensor according to the present invention is able to isolate individual vector components of electromagnetic fields. Sensors of the present invention measure two components of an electromagnetic field within a plane, essentially at the same point. Sensors of the present invention may also be arranged to measure three components of an electromagnetic field within a localized area about a central point. Because these sensors may have a small sensitive area, these sensors permit high-resolution electromagnetic field mapping. Sensors of the present invention may also be manufactured using planar technology, further permitting integrated sensor arrays for mapping fields without the need to scan test specimens. These sensors also allow the design of eddy current probes, and arrays of probes, for nondestructive testing and metallic profilometry, thus permitting new methods of detection of defects using these probes and arrays of probes.
One embodiment, for example, is substantially only sensitive in one direction. This embodiment has little to no response to electromagnetic fields in directions other than this single, sensitive direction. Sensors of the present invention, therefore, yield much more precise measurements of electromagnetic fields. Sensors of the present invention also exhibits a linear response and constant sensitivity over a wide range of frequencies, from DC to the megahertz domain. Because such sensors may be manufactured on silicon substrates, embodiments may be very small with high spatial resolution. Silicon substrate technology also allows many sensors to be manufactured on a single wafer. Sensors of the present invention are, therefore, small, precise, and inexpensive.
Another embodiment includes at least two coplanar magneto-resistive sensors. This embodiment measures two components of an electromagnetic field within a plane. Each magneto-resistive sensor measures the electromagnetic field along a sensitive axis in the plane of the at least two magneto-resistive sensors. The at least two magneto-resistive sensors may be orthogonally arranged to measure orthogonal components of the electromagnetic field in an area of intersection of the sensitive axes.
A further embodiment describes a product for measuring an electromagnetic field in two dimensions. This embodiment includes a first and a second magneto-resistive sensor. The first and second magneto-resistive sensors have a coplanar relationship and are arranged in a cruciform about a central point. The first magneto-resistive sensor has a first sensitive axis in the plane and measures the electromagnetic field along the first sensitive axis. The second magneto-resistive sensor has a second sensitive axis in the plane and measures the electromagnetic field along the second sensitive axis. The first and second magneto-resistive sensors measure orthogonal components of the electromagnetic field in an area of the central point.
Still another embodiment describes an electromagnetic product for measuring electromagnetic fields. The electromagnetic product has a plurality of devices, with each device comprising at least one pair of coplanar magneto-resistive sensors. Each magneto-resistive sensor has a sensitive axis in the plane and measures an electromagnetic field along the sensitive axis.
Another embodiment describes an electromagnetic product for measuring an electromagnetic field in three dimensions. This embodiment has at least two coplanar magneto-resistive sensors, with each magneto-resistive sensor having a sensitive axis in the plane of the at least two coplanar magneto-resistive sensors. A third sensor is sensitive to the electromagnetic field in a direction perpendicular to the at least two coplanar magneto-resistive sensors. The third sensor may utilize the Hall effect to measure the electromagnetic field.
Alternative embodiments describe a product for measuring electromagnetic fields. This product includes a plurality of devices arranged in a stack. Each device in the plurality of devices comprises at least one pair of coplanar magneto-resistive sensors, each magneto-resistive sensor having a sensitive axis in the plane of the device and measuring an electromagnetic field along the sensitive axis. The product measures the electromagnetic field at multiple locations within the stack. The plurality of devices may be arranged in a two-dimensional planar array, such as a sheet, or even a stack of two-dimensional planar arrays.
A further embodiment describes a product for mapping electromagnetic fields. This embodiment has at least two coplanar magneto-resistive sensors, each magneto-resistive sensor having a sensitive axis in the plane and measuring an electromagnetic field along the sensitive axis. The at least two magneto-resistive sensors are arranged about an area of intersection of the sensitive axes. A coil, carrying a current, biases each magneto-resistive sensor or compensates for background fields. The product maps magnitude and direction of the electromagnetic field in the plane. One or more magnets may also be used for biasing each magneto-resistive sensor.
Embodiments also include a product for detecting flaws in specimens. The product has a coil and at least two coplanar solid-state magnetic sensors and a third sensor. The coil induces an electromagnetic field in the specimen. The at least two coplanar solid-state magnetic sensors are arranged exterior to the coil, wherein the flaw creates a perturbation in the induced electromagnetic field, and the at least two solid-state magnetic sensors detect this perturbation to indicate the flaw. The at least two solid-state magnetic sensors may include giant magneto-resistive (GMR) sensors, spin-dependent tunneling (SDT) sensors, anisotropic magneto-resistive (AMR) sensors, and Hall effect sensors. The coil may have a cylindrical configuration surrounding the two coplanar solid-state magnetic sensors. The coil could also have a flat configuration, placed exterior to the sensor, and optionally centered about a central point. A probe that utilizes a one-directional spin-dependent tunneling (SDT) sensor, for example, could comprise a flat coil placed exterior to the sensor and centered about the sensor.
Still a further embodiment describes a product for mapping flaws in specimens. A coil induces an electromagnetic field in a specimen. At least two coplanar magneto-resistive sensors each measure the induced electromagnetic field along a sensitive axis in the plane. The at least two magneto-resistive sensors are arranged to measure the induced electromagnetic field in an area of intersection of the sensitive axes, wherein a flaw creates a perturbation in the induced electromagnetic field, and the at least two magneto-resistive sensors detect this perturbation to map the flaw. The area of intersection typically includes the active area of each sensor.
Still another embodiment discloses a product for mapping flaws in specimens. A coil induces an electromagnetic field in the specimen. A first magneto-resistive sensor and a second magneto-resistive sensor have a coplanar relationship and are orthogonally arranged. The first magneto-resistive sensor measures the induced electromagnetic field along a first sensitive axis in the plane. The second magneto-resistive sensor measures the induced electromagnetic field along a second sensitive axis in the plane. The first and second magneto-resistive sensors measure orthogonal components of the induced electromagnetic field in an area of the central point. A perpendicular sensor measures perturbations in the induced electromagnetic field in a direction perpendicular to the plane of the at least two coplanar magneto-resistive sensors. The flaw creates a perturbation in the induced electromagnetic field, and the orthogonal arrangement of the first and second magneto-resistive sensors detects orthogonal components of this perturbation, and the orthogonal components map the flaw. The product, having the first and the second magneto-resistive sensors, enables the mapping of a randomly-oriented crack or determining the orientation of a crack having an unknown orientation.